*{
    margin: 0;
    padding: 0;
}
.box{
    display: flex;
    /* 对齐方式 两端对齐 */
    justify-content: space-between;
    
}
span{
    flex: 1;
    text-align: center;
    line-height: 40px;
    font-size: 20px;
    font-weight: 700;
    border: 1px solid #666666;
}
.router-link-active{
    background-color: red;
}
.nav{
    text-align: center;
}